Process for peeling potatoes

ABSTRACT

The potato peel is loosened by a double treatment with hot lye solution, each treatment being followed by a holding period. The potato is subsequently exposed to radiant heat and the loosened peel is removed in the dry state by brushing.

United States Patent. 1 9] Huxsoll et al.

[ 11 3,759,160 Sept. 18,1973

[ PROCESS FOR PEELING POTATOES {75] Inventors: Charles C. Huxsoll;Robert P.

Graham, both of El Cerrito; Merle L. Weaver, Martinez, all of Calif.

[73] Assignee: The United States of America as represented by theSecretary of Agriculture, Washington, DC.

[22] Filed: Aug. 11, 1971 [2]] Appl. No.: 170,939

[52] US. Cl. 99/2333 [51] Int. Cl....- A23n 7/02 [58] Field of Search146/231, 235, 232;

Primary Examiner-Willie G. Abercrombie Att0meyR. Hoffman et al.

[57] ABSTRACT The potato peel is loosened by a double treatment with hotlye solution, each treatment being followed by a holding period. Thepotato is subsequently exposed to radiant heat andthe loosened peel isremoved in the dry state by brushing.

5 Claims, 1 Drawing Figure POTATOES DIP IN HOT LYE SOLUTION HOLD TOLOOSEN PEEL DIP lN HOT LYE SOLUTION HOLD TO 4/4 LOOSEN PEEL RodionlHecIIer DIP IN SULFITE SOLUTION Feed (OPTlONALl PRODUCT (PeeledPotatoes) PAIENTEII EPI 3.759.160

POTATOES DIP IN HOT LYE SOLUTION HOLD TO LOOSEN PEEL W2 DIP IN HOT n/3LYE SOLUTION HOLD TO /V4 LOOSEN PEEL PROCESS FOR FEELING POTATOES Anon-exclusive, irrevocable, royalty free licensein the invention hereindescribed, throughout the world for all purposes of the United StatesGovernment, with the power to grant sublicenses for such purposes, is

hereby granted to the Government of the United States of America.

This invention relates to and has among its objects the provision ofnovel processes for peeling potatoes.

More particularly, the invention provides procedures.

which not only give efficient peeling results but also which form wastematerial which is readily disposable. In addition, the processreducesshattering during'subsequent cutting operations. Further objectsof the invention will be evident from the following description whereinparts and percentages are by weight unless otherwise specified.

The FIGURE in the annexed drawing is a schematic diagram or flow sheetof the process of the invention.

In conventional practice in food processing plants, potatoes are peeledby applying the followingprocedure: The potatoes are immersed in hot lyesolutione.g., a solution containing about percent NaOH and maintained atabout l80-200 F. The potatoes are held in the lye solution until thepeels are softened and loosened. Then, the tubers are removed andsubjected to strong jets of water while rotated or tumbled about toexpose all surfaces to the jets whereby the lyeloosened skin is flushedoff the tubers. Although this procedure provides effective peeling, ithas the disadvantage that it produces a large volume of wash watercontaining organic matter and sodium hydroxide. The disposal of thiswaste liquor presents a serious problem. If discharged directly into astream it causes pollution of the water course. Moreover, biologicaldestruction by ponding or the like is slow and inefficient, particularlybecause of the high alkalinity of the liquor. Of course, the liquorcould be neutralized but this would involve additional expense for acidand for equipment for metering the acid and maintaining a predeterminedpH. Because of the present emphasis by federal, state,

and local governments on pollution control, food processors who rely onthe procedure in question are facing a crisis-they must devise adisposal system which" not only meets anti-pollution standards, but alsodoes the job economically so that they can stay in business. A failureto meet these criteria means that the operations must be shut down.

ln a previous US. Pat. No. (3,517,715 by Graham, Huxsoll, Hart, andWeaver, hereinafter referred to as 715) a process was described wherebypotatoes were peeled in the dry state. This process involved an initialtreatment with lye followed by heating with radiant heat andremoval, ofthe loosened peel by dry-brushing. lndeed,"7l5 obviated some of theproblems outlined above by eliminating the conventional step of removingthe lye-loosened peel with water, thereby reducing caustic usage andpeel loss. However, certain other problems remain. These include thedeleterious effects of shattering and the difficulty in removing thegreen layer without destruction of a iarge portion of the potato flesh.

A primary object of the invention is the provision of peeling methodswhich obviate the problems outlined above. A particular feature of theinvention is the sub stantial reduction of caustic usage and peel lossin comparison to 715 as well as conventional methods. Said reduction isobtained by employing two lye-dipping steps, each followed by a holdingperiod. The sotreated potato is then subjected to infrared heating andpeeled by dry-brush techniques.

The primary advantage of the invention is the large reduction in theamount of sodium hydroxide consumed in the lye treatment. Thedegradation of the peel is promoted by the action of lye on the cellularmaterial. The invention overcomes excessive use of lye in the followingway: The first lye treatment deposits a thin film of caustic on and inthe surface layers of peel tissue. Then, the potato is held for a periodof time to allow the lye to penetrate and attack said tissue. The potatois again subjected to hot caustic to supplement the first treatment.Finally, the so-treated potato is held for a period of time to completethe cellular destruction. In previous processes much more concentratedlye solutions were required because disintegration of the peel resultedsolely from the strength of the caustic. The present invention iseffective because of its combination 'of lye-dipping steps and holdingperiods, said combination providing a menas for metering an' amount oflye necessary (but not excessive) to loosen the peels. Thus, peeling isaccomplished with a minimum expenditure of caustic. In addition, sincemuch less concentrated caustic is necessary for the peeling, less lye islost due to the actual physical adherence of droplets to the surface ofthe potato. By application of the invention the amount of causticconsumed during operations is reduced by about a factor of 4 from about0.2 to 0.6 lb. of sodium hydroxide per 100 lbs. of potato 0.05 to 0.1lb. of sodium hydroxide per lOO lbs. of

potatoes (loss occurring in the invention). Since the cost of lye is amajor contributor to the total expenses incurred by the processor, thesavings to the potato industry will be substantial.

As with 715, the process of the invention does not yield a liquid wastematerial. It yields a solid waste which can be converted to feed forlivestock or other useful products.

In addition, the process of the invention provides effective peeling sothat the peeled tubers are adapted for all conventional uses as inpreparing dehydrated, prefried frozen, canned, and other potatoproducts. The peeling losses usually average only about 3 to 9 percentdepending on the age of the potato. The invention also provides forbetter removal of eyes and other defects for a given amount of peelloss.

Another advantage of the invention is that it reduces shattering and is,therefore, superior to all other potato-peeling processes including 715.Shattering occurs at times as a result of the high turgidity of certaintubers. After the potatoes are peeled, they are cut into pieces, forexample, strips for-French fries, etc. Shattering usually occurs duringcutting as the tubers are contacted by the blade and leaves the potatoeswith crack marks throughout. Usually, such minor crevices giveundesirable dark-colored lines and absorb excess oil when the potatostrip is fried. However, in extreme cases the strips break along theshattering lines and the product is useless.

Stillanother advantage of the invention is that the green layer, foundrandomlydispersed along the surface of non-mature potatoes, iseffectively removed. If not removed. said layer can lead to anundesirable product. The problem is that the green layer is veryresistant to the action of caustic, while the peel of the immature tuberis delicate and very little vlye is needed to loosen same. By employingthe techniques of the invention, removal of the green layer isaccomplished with minimum destruction of the fleshy tissue of thepotato. Removal of a large portion of such fleshy material in certainareas so that holes remain is known in the art as cratering."

In a practice of the invention, pototoes are first contacted withaqueous lye (NaOl-l). This is best done by immersing the tubers in thelye solution. Alternatively, the lye solution may be applied byspraying, brushing, or the like. Generally, the solution will containabout 1 to 10 percent of NaOFl. The concentration of caustic depends onthe maturity of the tubers to be peeled. Freshly harvested potatoes havethin skins, and defects such as eyes are not very deep. Consequently,only a minimum amount of lye is needed to loosen the peel. Thus, thepotato is dipped in about 1 to 10 percent hydroxide for approximately5-30 seconds. On the other hand, tubers which have been stored havethicker skins and deeper defects, thus necessitating the use of about5-l percent sodium hydroxide for a period of approximately 30-60seconds. In both cases the caustic is kept hot, i.e., at about l50-2l 2F. so it will penetrate rapidly into the corky tissue of the peel. As ageneral rule, the conditions should be adjusted such that theconcentration of lye and the temperature are as low as possible toproduce the desired peeling.

Next, the lye-treated potatoes are held at ambient temperature for aperiod of approximately 30-60 minutes to allow the lye time to destroythe peel tissue. Alternately, the potatoes may be either maintained inwarm air or heated with steam. If the former conditions are used, thetemperature of the warm air may be varied over a wide range. However,good results are attained at about l20-l60 F. The warm air dries thecaustic on the surface, thereby increasing the caustic concentration.Additional heat applied to the peel during the warm air treatmentfurther accentuates the degradative action of the lye. If the latterconditions are employed, the potatoes may be heated with steam at aboutl00-l 50 F. for about -30 minutes. Often, it is desirable to hold thepotatoes at ambient temperature for about 3 to 5 minutes prior to andimmediately after the treatment with steam. in this way the lye canpenetrate the peel tissue and the application of steam will not dilutethe caustic, thereby decreasing its disintegrative powers. Theparticular conditions employed are again subject to the maturity of thetubers, more severe conditions being necessary to loosen the thick peelof mature potatoes.

After said holding period, the potatoes are again treated with caustic.In this case the potatoes are dipped in about 2-10 percent sodiumhydroxide at about l50-2l2 F. for approximately 30-60 seconds. Thestrength of the lye is dependent on the severity of the conditions ofthe first lye treatment. Generally, if the lye solution in the firststep is concentrated, the amount of caustic necessary in the secondtreatment is small and vice versa. Moreover, the quantity of lye in thisstep should be as low as necessary to finish the destruction of thepeel.

The so-treated potatoes are subjected to another holding period fromapproximately 1-10 minutes, usually at ambient temperature. This stepallows the sec- 0nd lye treatment to be most effective in loosening theremainder of the peel.

Next, the lye-treated potatoes are exposed to radiant heat supplied, forexample, by conventional radiant heaters which provide elements broughtto incandescence (i.e., at least 1,200 F.) by electrical power, or bycombustion of propane or other gaseous or liquid fuels. Particularlypreferred are the modern gas-fired devices used for heating patios,outdoor restaurants, etc. These heaters include a porous ceramic platetreated with a catalyst. Propane or natural gas is fed through the plateand burns over the entire surface thereof, bringing the plate toincandescence and thereby providing a large area from which radiantenergy is uniformly emitted. Since radiant energy is effective only whena line of sight between source and the area to be heated is established,it is necessary to provide some arrangement to ensure that all points onthe surfaces of the potatoes come into such relationship with theradiant source. For example, one may provide a drum within which islocated a radiant heater. The lye-treated potatoes are fed into the drumwhich is then rotated. As the drum rotates the potatoes roll and tumbleabout so that all surfaces thereof are exposed to the energy emitted bythe radiant source. Another plan is to convey the lye-treated potatoesunder a bank of radiant elements while the potatoes are supported on aconveyor equipped with rollers, vibrators, or other suitable means toroll or tumble the tubers so that uniform exposure of all surfaces willbe attained.

By exposure of the lye-treated potatoes to radiant heat, variousdesirable effects are attained-the peel is heated, moisture in the peelis evaporated, and the lye solution in and on the peel is concentrated,i.e., made more caustic. These effects co-act to expedite hydrolyticdestruction of the binding substances in the peel and those which holdthe peel to the flesh. The net result is that the potatoes are rapidlybrought to a state where the peel is in a loosened state so that it canreadily be removed. The time of exposure to radiant energy required toachieve this state will vary depending on several factors such as thevariety of potatoes, the maturity thereof, and particularly the amountof radiant energy applied to the tubers. The proper time for a specificbatch of potatoes exposed to a particular radiant source is readilydetermined by testing the tubers at intervals and discontinuing thetreatment when the peels are loose and readily removable. In many casesthis can be done by observation, since when the potatoes appear dry onthe surface they are ready for the next operation. A critical factor isthat the treatment should not be so severe as to cause charring orburning of the peel. If this occurs at least part of the peel isconverted into a black smudgy material which becomes smeared over thetubers during the subsequent operation (peel removal). In other words,when it is attempted to remove the charred peel by applying friction theequipment becomes smeared with the clinging sooty char which is thentransferred onto the surface of r the peeled tubers. The net result isthat the peeled potatoes are not clean-as they are when the conditionsof radiant heat application are limited to attain peel loosening-but aredirty. They are stained with deposits of sooty material. Accordingly, insuch case washing with water is essential to obtain a satisfactoryproduct. In sum, where charring takes place, peel removal in the drystate is not feasible and one must resort towashing w th it .ettsnqctprslsa sreels spn s isn procedures. Moreover, there is the matter offlavor. When charring occurs various empyreumatic substances areproduced which exhibit most disagreeable odors and tastes. The potatoflesh absorbs some of these offensive substances with the result thatthe product is substandard -it exhibits foreign odor and taste andcannot be used until it is pared to remove the tainted layers of flesh.

After application of radiant heat as above described, the potatoes aresubjected to frictionfor example, brushingapplied in the dry state.Excellent results are obtained by contacting the potatoes with arotating cylinder, the surface of which is covered with protrudingfingers of soft rubber, Neoprene, or other elastomer. The non-abrasivebrushing effect obtained by the action of these fingers striking againstthe tubers causes the loosened peel to be dislodged quickly and withoutremoval of any significant amount of potato flesh. Moreover, the peelingaction is so effective that even the peel at indented areas (eyes) isremoved. For largescale operations, one may provide several drums(provided with soft rubber fingers) arranged with their axes parallel,and driven in such manner that each adjacent pair of drums rotate inopposite directions. By applying the treated potatoes to such anarrangement the tubers are continuously rolled and tumbled while beingbrushed by the rubber fingers, and the loosened peel is quicklydislodged. I

Following removal of the peels the potatoes may be given a dip in dilutesulfite solution to prevent discoloration of the tubers.

The practice of the invention is further illustrated'by the annexeddrawing. Referring thereto, the potatoes to be peeled are first dippedin hot lye solution 1 and then held in unit 2 to loosen the peel and toraise the temperature of the center of the potato so that shattering isreduced. The so-held potatoes are dipped in hot lye solution 3 and heldin unit 4 to complete the loosening process. From 4 the potatoes areintroduced into radiant heating unit 5. This unit includes a drum 6 ofperforated metal, supported and rotated by rollers 7. Within drum 6 islocated a radiant heater 8 which directs radiant energy downwardly. Asdrum 6 rotates, the lyetreated potatoes are rolled and tumbled about sothat all surfaces are exposed to the radiant energy. After this, thepotatoes are fed to the peeling unit, generally designated as 9, whichincludes rollers l0, l1, and 12, each driven in the directions indicatedby the arrows. The surface of each of the rollers is covered withprotruding fingers 13 of soft rubber. In a typical installation whereinrollers l0, l1, and 12 have a diameter of about 8 inches, excellentpeeling effects are obtained where rollers 10, 11, and 12 are rotated atabout 450-600 rpm. In a preferred arrangement, rollers 10, 11, and 12are arranged with their axes parallel and sloping so that the potatoeswill gradually be conveyed from the high end of the tier of rollers tothe low end, while being brushed and tumbled about by the coaction ofthe rollers and thereby producing a clean, peeled product. Afterpeeling, the potatoes may be given a brief dip in sulfite solution toprevent discoloration. The peeled potatoes are then ready for processinginto any selected end product by conventional procedures. Suitabletrays, pans, or the like may be positioned beneath rollers 10, l l, and12 to receive the bits of peel brushed off the potatoes. Ordinarily,some peel is detached from the potatoes during the treatment in radiantheater unit 5, and this refuse material may be likewise collected intrays or pans. As noted above, the removed peel is a granular meal whichcan be readily collected.

EXAMPLE 1 The invention is further demonstrated by the followingillustrative example.

Potatoes (U.S. l Russet Burbank, 0-1 month old) were weighed and thendipped in an aqueous solution of 5 percent sodium hydroxide at 190 F.for 30 seconds. The potatoes were removed from the bath and held 1 hourat ambient temperature. Then, the tubers were dipped in 5 percent sodiumhydroxide at 190 F. for 30 seconds, removed from the bath, and held atambient temperature for 3 minutes. The so-treated potatoes were placedin a rotating drum made of perforated metal and mounted with its axishorizontal. A propanefired radiant heater having a power output of30,000 B.t.u. per hour was positioned within the drum, and oriented sothat the radiant heat was directed against the potatoes which were thentumbled about at the bottom of the drum. Exposure to the radiant heatwas maintained for about seconds.

The treated potatoes were then subjected to brushing by the action of arotating drum, the surface of which was covered with protruding softrubber fingers. The peel-including that in the eyes--was quickly andeffectively removed by this brushing action. Weighing of the productindicated that the average peeling loss was 4 percent. The consumptionof sodium hydroxide was determined by standard procedures and expressedin pounds per pounds of potatoes.

The aforementioned experiment was repeated for several types ofpotatoes, namely U.S. 1 (2-4 months old), U.S. 1 (68 months old), U.S. 2(68 months old), and freshly-harvested Russet Burbanks, the peels ofwhich were largely green. The conditions in each case were varied. Theresults are summarized below.

Con- Peel sumploos, tion of Type of potato First dlp First hold Seconddip Second hold Heat percent NaOH 1 0. old 5" NaOH, 1hr. ambicnt 57NaOH, 3min. ambient. 1min 4.0 0.05 US #1 Russet Burbank (0 1m /iuo F. 30(190 F. 30

0 sv l f oH d d 4 o 0 07 5" NaOlI, .....do a o o US #1 (2 tmos. old)Aigo Fl, 1 390 F, 1

min. min. H d d 9 3 0 08 i 10" NnOll 30 min, mnbicnt 5'7 NnO N... o o...US #2 (tr-811105. old). (80 t 50 SH?- S00.

1'), NnOll, l I111,ambient... NaOIl, do ..(lo 3.7 0.08 ltussuts (Huull).I 1150 F" I5 190 F" 30 SW )1! d a 7 5 0 03 l i 10 Nnoll, 10 min. I 5'7,Nut 0 0.. i b #1 w mm Jim" in, 30 air; 26 min., iu0 1 :io

soc. ambient. soc.

\ Lbs/100 lbs. potatoes. 2 No oratering, good removal of green layer.

Having thus described our invention, we claim:-

I. A process for peeling potatoes, which comprises a. applying a hot lyesolution to unpeeled potatoes,

b. holding the so-treated potatoes at ambient temperature for about30-60 minutes,

c. Applying a hot lye solution to the potatoes, said solution being at atemperature essentially the same as that of the lye solution in Step a,

d. holding the so-treated potatoes at ambient temperature for about 1-10minutes,

e. exposing the said potatoes to radiant heat, and

f. removing the loosened peels by non-abrasive dry brushing.

2. The process of claim 1 wherein Step a is carried out under thefollowing conditions i. the concentration of lye is about 1 to 10percent,

ii. the temperature of the lye solution is about 150-212 F., and

iii. the duration of application of the lye solution is about 5 to 60seconds.

3. The process of claim 1 wherein Step c is carried out under thefollowing conditions i. the concentration of lye is about 2 to percent,ii. the temperature of the lye solution is about 150 to 212 F., and iii.the duration of application of the lye solution is about 30 to 60seconds.

4. A process for peeling potatoes, which conprises a. applying a hot lyesolution to unpeeled potatoes,

b. holding the so-treated potatoes about 3 to 5 minutes at ambienttemperature, then about 5-30 minutes during which time steam is appliedto them, and then about 3-5 minutes at ambient temperature,

c. applying a hot lye solution to the potatoes, said solution being at atemperature essentially the same as that of the lye solution in Step a,

d. holding the so-treated potatoes at ambient temperature for about 1-10minutes,

e. exposing the said potatoes to radiant heat, and

f. removing the loosened peels by non-abrasive dry brushing.

5. A process for peeling potatoes, which comprises a. applying a hot lyesolution to unpeeled potatoes,

b. holding the so-treated potatoes about 10-20 minutes in warm air atabout -160 F.,

c. applying a hot lye solution to the potatoes, said solution being at atemperature essentially the same as that of the lye solution in Step a,

d. holding the so-treated potatoes at ambient temperature for about 1-10minutes,

e. exposing the said potatoes to radiant heat, and

f. removing the loosened peels by non-abrasive 'dry brushing.

2. The process of claim 1 wherein Step a is carried out under the following conditions -i. the concentration of lye is about 1 to 10 percent, ii. the temperature of the lye solution is about 150*-212* F., and iii. the duration of application of the lye solution is about 5 to 60 seconds.
 3. The process of claim 1 wherein Step c is carried out under the following conditions -i. the concentration of lye is about 2 to 10 percent, ii. the temperature of the lye solution is about 150* to 212* F., and iii. the duration of application of the lye solution is about 30 to 60 seconds.
 4. A process for peeling potatoes, which conprises -a. applying a hot lye solution to unpeeled potatoes, b. holding the so-treated potatoes about 3 to 5 minutes at ambient temperature, then about 5-30 minutes during which time steam is applied to them, and then about 3-5 minutes at ambient temperature, c. applying a hot lye solution to the potatoes, said solution being at a temperature essentially the same as that of the lye solution in Step a, d. holding the so-treated potatoes at ambient temperature for about 1-10 minutes, e. exposing the said potatoes to radiant heat, and f. removing the loosened peels by non-abrasive dry brushing.
 5. A process for peeling potatoes, which comprises -a. applying a hot lye solution to unpeeled potatoes, b. holding the so-treated potatoes about 10-20 minutes in warm air at about 120*-160* F., c. applying a hot lye solution to the potatoes, said solution being at a temperature essentially the same as that of the lye solution in Step a, d. holding the so-treated potatoes at ambient temperature for about 1-10 minutes, e. exposing the said potatoes to radiant heat, and f. removing the loosened peels by non-abrasive dry brushing. 